1. Field of the Invention
This invention relates to novel vegetable based edible films which can be used in the processing of meat products, particularly as sausage casings.
2. Description of the Prior Art
Traditionally, edible sausage casings have been manufactured through a process of extrusion into a tubular hose material made of regenerated beef collagen. A conventional synthetic or natural casing is formed as a long, continuous tube which is drawn from a supply source.
In order to use the casing efficiently and effectively, an individual length of the hose material drawn from the source is “shirred” (gathered up longitudinally). This allows a large quantity of casing to be folded and positioned in a sausage or food packing machine for subsequent controlled unfolding as required as the casing material is filled with product. The shirring of casings for meat products such as sausage is well known in the food processing art. Two typical examples of the numerous prior art patents disclosing equipment for the shirring of casing are afforded by U.S. Pat. No. 4,580,316 (Günter) and U.S. Pat. No. 4,683,615 (Thomczak et al).
Increasingly, it has been sought to prepare food sealing and packaging materials comprising only non-animal based natural materials, owing to dietary and other considerations. U.S. Pat. No. 5,620,757 (Ninomiya et al) describes a multilayer heat-sealable edible film for sealing and packaging materials like powdered soup, flavoring oil, dried vegetables, etc., which comprises a water-soluble polysaccharide film layer (chiefly carrageenan, a polyhydric alcohol and water) and a subfilm layer containing a combination of soybean protein and gelatin.
U.S. Pat. No. 6,730,340 (MacQuarrie et al) describes edible casing film formulations incorporating carrageenan in conjunction with konjac and/or Gellan gums. Such a film, in a typical application, is wrapped around a meat substrate (turkey, ham, chicken) and the wrapped meat dried in a convection oven, until a protein skin is seen to form. Cooking is then completed in a steam cooker. The film exhibits a number of desirable properties, including pleasing edibility and imparting an appealing surface appearance to the cooked product.
However, despite the evident desirability of doing so, it has not been possible commercially to prepare non-animal meat casings using standard sausage production technology based on a shirred tubular casing. Because of their abundant availability and presence in many food products, starch or flour would appear to be the ideal raw material for all-vegetable based sausage casing. However most gum and starches do not exhibit the kind of phenoplastic properties which will allow the production of a homogeneous tube structure by extruding the polymer through a die set to an appropriate diameter, tube wall thickness, etc. U.S. Pat. No. 5,928,737 (Hammer et al) describes the extrusion into sausage casings of compositions based on natural starch which has been converted into an amorphous state by drying potato starch in vacuo, mixing with glycerol and kneading the mixture at an elevated temperature followed by extrusion and granulation to prepare a thermoplastic starch composition. This must additionally be compounded with gelatin and chitosan in order to be extrudable. However, this material, too, has not proven useful using standard sausage production technology based on a shirred tubular casing.
Some high-amylose starches have been successfully extruded into sheets and tubing or various dimensions, but such systems require inconvenient higher than atmospheric pressures to effect complete hydration of the polymers. Moreover, the finished products have typically been found to be too brittle and otherwise unsuitable for use as sausage casing.
The aforementioned U.S. '757 and '340 patents and many others take advantage of the well known film-forming abilities of starches and gums. Typically, these films are formed from a liquid slurry of the gums/starches in water, which is then cast upon a hot surface until sufficient water is thereby removed to produce the end film. However, only flat foils can be produced by this casting system, which are not suitable for the conventional production of tubes and other profile-type products.
While forming of a casing tube from a flat film section incorporating conventional hydrocolloids by folding the cast film into a tube and heat-sealing the edges was considered, the fact is that only a relatively narrow range of compositions is capable of being heat-sealed. Moreover, the intense heat necessary for effectively sealing a film to itself was found to cause excessive moisture loss in films of these compositions, leading to undesirable mechanical end properties, discoloration along the seal line and distortion of the body of the film.